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MB3778PFV-G-BND-EF (IC608) Study of DC/DC power MOS FET drive circuit
Power MOS FET : Vishay Siliconix product P-Channel MOS FET : Si3457DV (CP260P470A11) (IC607,
IC609)
[Rating]
V
DS
= -30V, I
D
(DC)= -3.4A (Ta=70˚C), I
D
(PULSE)= -10A, P
D
= 1.3W (Ta=70˚C)
[Specifications]
on resistor R
DS(on)
= 0.1
Ω
(V
GS
= -4.5V, I
D
= -3.4A)
t
d
(on) = 15nsec (Max.)
t
d
(off) = 50nsec (Max.)
C
iss
= 11000nsec
The turn On + turn Off time is 65nsec, and is sufficiently small compared to the switching cycle
5000nsec (oscillation frequency 200kHz). (There is little switching loss.)
When switching is On, the power MOS-FET gate charge is pulled by the open collector transis-
tor (base Hi) built-in the DC/DC IC (MB3778) to set the gate voltage V
GS
to 12V- (V
CE(sat)
+V
F
).
(The DC/DC open collector transistor operates actively, so the power MOS-FET turns ON at a high speed.)
On the other hand, the turn OFF time slows during OFF due to the open collector's pull-up
resistor R1 (base L
o
). To charge the power MOS-FET gate, Tr1 in this drive circuit turns ON
when the base voltage has been increased by 0.6V in respect to the emitter by the pull-up
resistor R1. It then turns OFF at a high speed as the power MOS-FET gate is charged by Tr1's
active operation.
(Tr1 can be turned OFF at a high speed because the pull-up resistor is bypassed.)
The drive circuit consumes power only when the consumption power is turned ON and OFF by
the Tr1 and R2, and thus can be ignored. When the power consumed by the pull-up resistor
R1 during ON is considered, the following is attained.
Current consumption (during ON) = (12-V
CE(sat)
)V / 3.3k
Ω
= 3.3mA
Power consumption = 3.3mA (at ON) x (12-V
CE(sat)
)V x 0.5 (On Duty) = 18mW
The DC/DC IC (MB3778) used with this circuit has a two-channel output, so there are two
driver circuits. The I
CC
of the DC/DC IC is 2.4mA, so the power consumption is 28.8mW
(=2.4mA x 12V), and the total power consumption including the driver circuit is 64.8mW
(=18mW x 2Ch+28.8mW).
10
MB3778
(IC608)
Output drive terminal
(Io
MAX
= 50mA)
(
)
7
+12V
Open corrector output
1/10W 3.3k-J
On time
At Off
V
CE (sat)
Max.:1.4V
Typ.:1.1V
D614, D615
V
F
= 0.3V (Typ.)
R1
R2
Corrector current Ic (1A/Div)
Voltage between Collector
and Emitter
V
CE
(5VDiv)
Collector loss
Pd
Tr1:2SC2412K-R (Q601)
Drain current (0.5A/Div)
Voltage between Gate and Source (5V/Div)
Power MOS-FET (IC607,IC609)
1/10W 10-J
Tr1:2SC2412K-R (Q601,Q602)
Summary of Contents for NEC MultiSync LCD1550X LCD1550X LCD1550X
Page 88: ...SCHEMATIC DIAGRAM POWER LCD1550X Normal Power Save 1ch Pin 4 2ch Pin 1 3ch Pin 2 4ch Pin 5...
Page 89: ...SCHEMATIC DIAGRAM PWB MAIN POWER LCD1550X...
Page 90: ...SCHEMATIC DIAGRAM PWB MAIN INPUT LCD1550X...
Page 91: ...SCHEMATIC DIAGRAM PWB MAIN SYNC LCD1550X...
Page 92: ...SCHEMATIC DIAGRAM PWB MAIN TMDS LCD1550X...
Page 96: ...SCHEMATIC DIAGRAM PWB MAIN ASIC LCD1550X...
Page 97: ...SCHEMATIC DIAGRAM INVERTER LCD1550X 1ch Q701 B 2ch Q702 B...
Page 98: ...SCHEMATIC DIAGRAM PWB SW LCD1550X...
Page 100: ...SCHEMATIC DIAGRAM POWER LCD1550X...
Page 101: ...SCHEMATIC DIAGRAM PWB MAIN POWER LCD1550X...
Page 102: ...SCHEMATIC DIAGRAM PWB MAIN INPUT LCD1550X...
Page 103: ...SCHEMATIC DIAGRAM PWB MAIN SYNC LCD1550X...
Page 104: ...SCHEMATIC DIAGRAM PWB MAIN TMDS LCD1550X...
Page 105: ...SCHEMATIC DIAGRAM PWB MAIN MC LCD1550X...
Page 106: ...SCHEMATIC DIAGRAM PWB MAIN ASIC LCD1550X...
Page 107: ...SCHEMATIC DIAGRAM INVERTER LCD1550X...
Page 108: ...SCHEMATIC DIAGRAM PWB SW LCD1550X...
Page 127: ...16 Document No VSPF A028 Bave Average brightness of 1 to 9 10 50 90 90 10 50 5 1 2 3 6 9 8 7 4...
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